1. Field of Art
The present invention relates to articles made on the basis of fibrous sheets for which it is useful or necessary to be able to provide, by prior ruffling, a local functional zone of limited possible elastic stretching.
The term sheet should be considered to cover all supports or substrates based on natural and/or synthetic fibers arranged in a structured manner as obtained by weaving or organized at random like the non-woven supports or carded, even slightly needled, cloth. Articles corresponding to such characteristics are used in numerous areas, in particular for diapers.
2. Prior Art
It is generally desired to be able to have one or more ruffling portions available so that the portion in question may find a faculty of adaptation, conformation or retention compatible with the object or objects envisaged.
Up to the present time, it was desired to comply with such requirements by resorting to different methods employing each time one or more longitudinally elastic yarn element.
One of the known methods consists in connecting the longitudinally elastic yarn element with the substrate by means of a bead or dots of adhesion of an intermediate adhesive product.
Such a technique raises considerable problems in implementation, particularly in continuous production installations, as it is necessary to be able to have available a particularly precise regulation of temperature for the deposit of the bead or dots of adhesive product to be able to intervene with local precision, without overflow, without extrusion, without clogging of the dispensing installation and with the deposited quantity just necessary, all these requirements and conditions having to be able to be maintained constantly for relatively high speeds of manufacture of the articles.
It is apprecitaed that such a regulation of temperature for deposits of small quantity raises a virtually unsolvable problem for the present technique.
Another drawback of this technique resides in the fact that the adhesive product is more or less sensitive to dust which, by its presence may be such as to disturb the connection by adhesion between the elastic yarn element and the substrate.
Another drawback of this technique resides in the fact that the adhesive product may migrate in detrimental manner through the substrate, particularly in the case of laminating, giving the article produced an ineasthetic, even aggressive appearance, when the substrate is to be placed in direct relation with the epidermis. Such a migration may also be the source of a lamination detrimental to the local function having to be assumed. Such is the case of the fecal barriers of fitted diapers whose efficiency is ruined if these barriers no longer present, by adhesion on the support, the freedom necessary to be raised substantially perpendicularly to the plane of the support by the action of ruffling of the elastic yarn element.
Another technique of the prior art consists in connecting the elastic yarn element and the support by means of stitching made so as to traverse the elastic yarn element locally or to imprison the latter on the substrate.
This technique is not satisfactory for different reasons.
The cost of producing the ruffled portions becomes, in certain cases and in particular for much-consumed disposable articles, expensive due to the low speed of production, the expense generated by the consumption of the connecting elastic element and by the frequent interruptions due to the ruptures of the elastic yarn element, to the necessity of refilling the reels dispensing the elastic yarn element, even to the changes of the stitching heads by reason of ruptures or breaks of the needles.
A particularly crippling drawback of this technology also resides in the consequence resulting from the work of the needles which are led to traverse and therefore to perforate the substrate or substrates having to be filled.
Such perforations represent unsurmountable and difficult obstacles in the case of watertight articles having to be made, as is the case for certain scientific domains or for the medical domain.
In order to overcome the drawbacks of the techniques mentioned above, Patent Application FR 2 532 337 proposes another technique which consists of employing a ruffling slide comprising a tubular sleeve defined by the substrate and, for exampe, the fold of one of its edges. Inside this sleeve, between the two sheets, there is disposed an elastic yarn element which is connected to the walls of the sleeve by spaced apart transverse connecting portions, defining therebetween tubular ruffling portions, inside which the elastic yarn element is free. The connecting portions also ensure assembly of the two sheets of the sleeve together.
Such a ruffling slide is made continuously, by means of an installation disposing the sleeve placed flat, in the extended state and placing in the latter the elastic yarn element subjected to a longitudinal stretching stress. The installation then forms, by heat-sealing or high-frequency welding, locally and in aligned manner, the local immobilizations of the elastic yarn element on and between the two sheets of the sleeve. After execution of this immobilization, the stress on the elastic yarn element is released, with the result that it presents a length shorter than that of the tubular portion included between two immobilizations and it consequently imposes thereon a ruffling of orientation substantially perpendicular to the general direction of the sleeve.
This latter technique does in fact bring a solution to the problems raised by the other known techniques, but nonetheless presents certain drawbacks resulting from the very nature of the connecting portions employed.
In fact, in accordance with Application FR 2 532 337, the connecting portions, which present a substantially rectangular shape, simultaneously ensure a welding between the two sheets constituting the sleeve and an adhesion of the elastic yarn element on each of its two sheets, with the result that it is not possible to ensure adjustment of the ruffling after manufacture of the slide. Moreover, the connecting portions alter the behaviour of the elastic yarn element, creating discontinuities in its structure. These discontinuities result in particular from the mechanical and thermal stresses due to the operation of welding of the elastic yarn element on the walls of the sleeve. Similarly, the alteration of tubular portions in which the elastic yarn element is free and of connecting portions at the level of which the elastic yarn element adheres to the walls of the sleeve, does not make it possible to benefit fully from the mechanical characteristics of the elastic yarn element which is divided, to some extent, into a succession of independent elastic elements acting only at the level of one tubular portion to ruffle this latter.